Blogroll

Correlation between column predicates

Multi column correlation

We all have encountered this situation many times before: Cost based optimizer assumes no correlation between two columns (until 11g) and this has the effect of reducing cardinality of a row source erroneously. Incorrect cardinality estimates
are one of the many root causes for SQL performance issues.

Well, okay, it is time to introduce myself. I specialize in Oracle performance tuning,
oracle internals and E-business suite. I have over 15 years of experience as an Oracle DBA, currently,
I am employed with pythian [ Thanks Paul]. I am regular presentor in major conferences such as
hotsos, ukoug, rmoug etc. I am also an Oaktable member.

Like this:

LikeLoading...

Related

This entry was posted on March 21, 2008 at 3:00 pm and is filed under CBO.
You can follow any responses to this entry through the RSS 2.0 feed.
You can leave a response, or trackback from your own site.

2 Responses to “Correlation between column predicates”

Kumarsaid

Hi Riyaz:
The presence of an index on n1, n2 is making a difference for cpu %cost column CREATE INDEX T_VC_IDX ON T_VC (N1, N2);. The cardinality estimate is still incorrect but which would be the weighing criteria in this case the %cpu cost, bytes or the cardinality.